1. Field of the Invention
The present invention relates to cameras and imaging devices, and more particularly to cameras for use in EMI sensitive environments.
2. Description of Related Art
During operation, all electronic devices radiate unwanted electrical signals known as electromagnetic interference (EMI). In general, unwanted EMI can be dealt with in two ways: either by electrical or circuit level modifications, or by physical shielding. Of course, a combination of both types can be used for a particular device as appropriate.
Electrical techniques include modifying the timing of clock signals by frequency modulation so that the spectral density is reduced. This technique is also called clock skewing. This does not lessen the overall energy of the emitted EMI, but it does reduce unwanted peaks that would block frequency channels needed for data communication, e.g., by radio transmitters used in a mobile telephone. At the circuit level, the length of a path that could act as an aerial to transmit or receive EMI can be minimized. The effectiveness of this technique is necessarily limited by the need to use high frequency clocks and signaling. Other circuit techniques exist such as the introduction of lossy components and low impendence paths to ground to suppress noise.
Physical techniques for suppressing EMI predominately involve encasing electronic components within shielding in the form of electrically conductive walls or ground planes. The shields can act to absorb EMI, or simply to reflect it back into the body of the device, depending on the type and quantity of material that is used.
A physical structure completely surrounding a cavity with electrically conductive walls is known as a Faraday cage. A Faraday cage shields its interior cavity from EMI by canceling EMI transmissions across the cage through electrical conduction. In practical application, most electrical devices need a way to send signals in and out, such as by means of a cable, so a complete Faraday cage cannot be used. Rather, a partial Faraday cage is typically used in which apertures through the electrically conductive walls allow for desirable signals to pass into and/or out of the electrical device inside.
In the case of shielded cameras, signals typically pass into and out of the housing by way of a cable connector. A partial Faraday Cage surrounding the electronic components of such a camera has a relatively large opening where the cable connector passes through the walls of the Faraday cage. The connector opening in a typical camera is large enough to provide a path for unwanted Radio Frequency (RF) emissions to radiate in and out of the camera housing. This can be problematic for cameras used in EMI sensitive applications, such as onboard aircraft, for example. Existing cameras have had difficulty passing the emissions and susceptibility requirements which are required for certification by the FAA or other governing authority.
Such conventional methods and systems generally have been considered satisfactory for their intended purpose. However, there still remains a continued need in the art for camera components that have improved performance in EMI sensitive environments. There also remains a need for such camera components that are easy to make and use. The present invention provides a solution for these problems.